In mammals, the subfamily II members CHD3 and CHD4 are subunits of NURD (nucleosome-remodelling and histone deacetylase) complexes, which contain histone deacetylases (HDACs) and function as transcriptional repressors68. Like BAF complexes, mammalian NURD complexes achieve diversity in regulatory function through combinatorial assembly (Fig. 1b). The core ATPase is CHD3 or CHD4. There are three main accessory subunits, which are encoded by gene families: MTA (metastasis-associated), MBD (methyl-CpG-binding domain) and RbBP (retinoblastoma-associated-binding protein). Each complex contains one MTA protein: MTA1, MTA2 or MTA3. These are mutually exclusive (see ref. 69 for a review) and nucleate complexes with markedly different, and sometimes opposite, functions. Each complex also contains MBD2 or MBD3, which are functionally distinct and contribute to different forms of the complex70, and RbBP4 and/or RbBP7. The composition of the NURD complexes varies with cell type and in response to signals within a tissue (see ref. 71 for a review), giving rise to a diversity of complexes with distinct functions.
